Peroxide-Substituted Polysilazanes: Self-Thermosetting Ceramic Precursors
J. Schwark
Silicon-based polymers such as polysilazanes and polycarbosilanes have been used extensively as ceramic precursos to silicon nitride and silicon carbide. A prerequisite for the utilization of such polymers for the formation of ceramic articles (e.g., molded articles, fibers) is that they undergo a transformation from a proecessible state (generally soluble or thermoplastic) to an infusibel state. This is necessary to prevent changes in the ceramic green (unfired) body during subsequent firing. Often, the green body is exposed to a reactive gas such as a chlorosilane or steam to partially crosslink the preceramic polymer and render if stable to pyrolysis. An altermative to this approach is to utilize low molecular weight, thermosettable polymers which become infusible solids by rapid crosslinking during the thermosetting process. This strategy has been used successfully at Hercules Incorporated to devleop a family of polysilazane-based precursors to both Si3 N4 and SiC with thermoset when heated in the presence of peroxides.